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  <title>Document</title>
</head>
<body>
  <script>
    let arr = [1,2,3,4,5,4,3,2,1]
    //数组去重
    // let result = [...new Set(arr)]
    // console.log(result)
    //交集
    let arr2 = [4,5,6,5,4]
    let result = [...new Set(arr)].filter(item => {
      let s2 = new Set(arr2) //456
      if(s2.has(item)){
        return true
      }else{
        return false
      }
    })
    //简写
    // let result = [...new Set(arr)].filter(item => new Set(arr2).has(item))
    // console.log(result)

    //并集
    let union = [...new Set([...arr, ...arr2])]
    console.log(union)
    //差集
    let diff = [...new Set(arr)].filter(item => !(new Set(arr2).has(item)))
    console.log(diff)
  </script>
</body>
</html>